Hydrazine recovery



IiF-eLS-WS Remi O 2,780,531 HYDRAZINE RECOVERY Richard N. Lewis, North Haven, Conn, assignor to 01in Mathieson Chemical Corporation, a corporation of Virginia V v No Drawing. Application February 23, 1954, 1

I Serial No; 412,051 1 8 Claims. torn-s12 invention relates generally to hydrazine and more" p r y to a novel afl'dimproved method r yby the various separation techniques discussed above.

drating aqueous solutions of hydrazine.

Hydrazine and water form aconstant-boiling mixture and, consequently, about 64 to 70 percent hydrazine is the maximum concentration that can be obtained as a residue from ordinary fractional distillation processes which involve vaporizing the water. It has been suggested that barium oxide, calcium oxide or sodium hydroxide be included in the distillant of such processes if more concentrated solutions are desired but fractional distillation processes require a high heat consumption to vaporize the water and only large and intricately designed fractionating columns equipped with apparatus for opera tion under vacuum can be utilized. Qn the other hand, the proposed method for separating hydrazine-from water 2,780,531 Patented Feb. 5, 1957 Hill Book Company, Inc., New York, 1951, may be used. A continuous extraction technique or an economical batch extraction technique will thereby be enabled.

An organic acid having an ionization constant of not more than that of hydroxybenzene, reported to be about 1.3)( at 25 C. in the Handbook of Chemistry and Physics, twenty-fifth edition, published by Chemical Rubber Publishing Company in July 1941, which doesnot react chemically with hydrazine and is substantially insoluble in an aqueous solution of hydrazine, can be utilized as the extractor for the hydrazine. Phenols such as hydroxybenzene and its lromologs having substituted alkyl groups are excellently suited for selectively dissolving hydrazine from an aqueous solution. The hydrazine in the phenol phase can be easily separated from the phenol More specifically, hydroxybenzene and its alkyl homologs having alkyl groups of one to eight carbon atoms such as, ortho butyl-hydroxybenzene, para tertiary butyl hydrox'ybenzene, the di-methyl hydroxybenzene (xylenols),

" ortho ethyl hydroxybenzene, meta ethylhydroxybenzene,

para ethyl-"hydroxybenzene, ortho propyl hydroxybenzene, meta propyl hydroxybenzene, para propyl hydroxybenzene, meta methyl hydroxybenzene, ortho methyl hydroxybenzene, para methylhydroxybenzene, para amyl hydroxybenzene, para tertiary amyl hydroxybenzene and the octyl by converting it to hydrazine sulfate and treating this 7 product with liquid ammonia requires a complexity of equipment and has ahigh .cost of raw materials. More- In accordance with this invention, the foregoing objects as well asothers are accomplished,'generally speaking, by providing a method for preparing hydrazine which involves extracting hydrazine from an aqueoussohit ion thereof with an organic acid having an ionization constant of not more than that of hydroxybenzeue and thereafter decanting the acid phase from the aqueous phase. The

hydrazine is then separated from the organic acid phase by various techniques. Among these techniques a straight distillation of the acid phase appears to be the most preferred. However, one may also enjoy a precipitation technique which involves the adding of an acid capable of precipitating hydrazine, such as hydrochloric, sulfuric, etc. to the acidphase and then filtering off the precipitate. The hydrazine isthen regenerated with the use of a base such as ammonia or solid alkali hydroxide. This latter technique using the decantation as a preliminary step is an improvement over the precipitation teachings of the prior art in that a better precipitation results. This follows from the fact that more concentrated solutions give better precipitations. 7 itself is the addition of an'alcohol to the phenol solution and subsequent distiliationvsuch as disclosed in copending application, Serial Number 384,513, filed October 6, 1953.

Obviously, the extraction technique 'of this invention will be more effective if more than one extraction is used. In this regard, spray towers, pack towers, bafile towers, perforated plate towers, asxdescribed in the book entitled Liquid Extraction, by Robert E. Treybal, McGraw- Another technique that suggests;

hydroxybenzenes are suitable for the purpose. The xylenols and the cresols, singly and combined as well as cresylic acid have been found to be particularly advantageous for extracting the hydrazine from an aqueous solution thereof.

In carrying out the invention in practice, it is preferred to employ a continuousprocess in which a suitable phenol, or a mixture of phenols is passed through a vertical contact vessel in a flow counter'to the flow, ofthe aqueous solution of hydrazine. In orderto obtain a large area of contact between the phenol and the aqueous solution,

the phenol may be injected through a small orifice into the stream of the aqueous hydrazine solution, or the hydrazine solution may be dispersed in a similar manner q into a stream of phenol, as performed when using a spray tower extractor (see Treybal, cited above). The large area of contact between the two phases facilitates absorp tion of the hydrazine by the phenol. The phenol-hydrazine phase leavingthe extraction apparatusiis then a; separated into its components by various techniques, pref:

efablyfa distillation is used. It is to be understood,how ever, that other techniques such as precipitation, azeo tropic distillation with alcohols, etc., may also be used.

Upon such separation of the hydrazine from the phenol, the phenol may be returned to the extraction column to be utilized again. The volume of solvent required to extract the hydrazine from the aqueous solution is, of course, dependent upon the solubility of the hydrazine in the particular solvent selected from the class of solvents suitable for the purpose. The extraction may be made at room temperature or any other convenient tempera- 'ture.

It has been found that meta methyl hydroxybenzene and cresylic acid are particularly advantageous for extracting thehydrazine from an aqueous solution thereof. In one example, an aqueous solution composed of about "6% hydrazine and about 94% water was extracted with meta methyl hydroxybenzene in the ratio of about 2.

parts thereof to one part'aqueous solution. The resulting meta methyl hydroxybenzene phase was separated from phase contained only about 5.2 parts water per part of hydrazine.

An aqueous solution composed of about 94.5% water and about 5.5% hydrazine was extracted with cresylic acid. The cresylic acid utilized was a mixture of phenols boiling from about 202 C. to about 217- C., a commercially available product. About 2 parts cresylic acid was utilized for each part aqueous solution. Theresulting cresylic acid rich phase contained about 2.6% hydrazine, about 12.4% Water and about 85% cresylic acid. The upper aqueous rich phase contained only about 1% cresylic acid; It is to be noted. that less than 5 parts water per part hydrazine was found in the meta methylhydroxybenzene rich, phase. This, water could be reand-b a s re is t a i In order further to clarify and better to describe the invention, the following is a detailed description of one i t iasn f be s About 178 parts of an aqueous solution containing about ll parts hydrazine is mixed with about 17Q,par ts meta methylhydroxybenzene and the mixture is agitated about minutes at about 20? C. The agitation is. discontinued and the two phases are permitted to segregate audare thenseparated by decantation. The lowerphase. contains about 545 parts hydrazine, about 32 parts water and about 167 parts meta methyl hydroxybenzenc- About 5.5 parts of the hydrazine is in the upperphase which; also contains about 135 partswater and about 3 parts [meta methyl hydroxybenzene. Extraction of the upper phajseis repeated with seven successive. similar volumes of meta methyl hydroxybenzene to remove substan: tially allofithe hydrazine therefrom and each of the phasesrich in meta methyl hydroxybenzene and hydrazine and containing a small amount of water aremixed with the aforesaid lower phase and the resulting solution is separated intoits components by techniques known to thoseskilled in the art, preferably a distillation tech: nique is used. Hydrazine isfound to come off-asa fraction of the distillate and is found to be either substantially anhydrous or of such concentration that a second distillation ot: that fraction will yield an anhydrous hydrazine. The meta methyl hydroxybenzene is recycled for a succeeding extractionprocess. 1

Theioregoing embodimentjis described in detail in-or der to illustrate the invention but variations will occur tothose skilled in the artand can be made withoutde: partingirom the spirit and scope of the inventionexcept as limited by the appended claims.

claimedand desiredv to besecured by Letters Patent isas 9 19;

;.'The. invention having thus beenv described,- what 1. An extraction process for dehydrating aqueous hydiaries. which comprises. mixing. an. organicacii having an ionization constant of not more than 1.3)(10- at C. with the aqueous hydrazine mixture and decanting a hydrazine-acid layer from the aqueous mixture.

2. An extraction process for dehydrating aqueous hydrazine which comprises; mixing. an organic acid having an ionization constantofi notmore thanthat of hydroxybenzene with the aqueous hydrazine mixture and decanting a hydrazine-acid; layer from the aqueous mixture.

3. An extraction processfor. dehydrating aqueous hydrazine which comprises mixing an organic acid having an aa en nstantofi ot me e h fiha fibenzene andthereafter separating the hydrazine and the organic acid with the aqueous hydrazine mixture and decanting a hydrazine-acid. layer fromthe aqueous mixture;

4. An extraction process for dehydrating aqueous hydrfazine which comprises mixing a phenolic compound with the aqueous hydrazine mixture andidecanting a hydrazine-phenol layer-from the aqueous mixture.

5;. An ext-ractionprocess for dehydrating aqueous hydrazine which, comprises mixing a. phenolic compound with theiaqueoushydrazine mixture and decanting a hydrazine-phenol layer from theaqueous mixture and thereafter separating. the hydrazine and the phenolic compound.

6. An. extraction process. for dehydrating aqueous hydrazine which comprisesmixing metamethyl hydroxybenzone ,with the aqueous hydrazine. mixture and decanting a; hydrazine-metaemethyl.hydroxybenzene layer from the aqueous mixture.

, extraction process fordehydrating aqueous hydrazine. which comprises. mixing. cresylic acid with the aqueoushydrazine mixture. and decanting: a hydrazinecresylic acid: layer from the. aqueous mixture. .8. A continuous extraction process for dehydrating aqueous hydrazine which comprisescontinuously adding an organic acid having an ionization constant of not more than 1 3 1.0- .:at 25. C. to the aqueous hydrazine mixture ina. continuous countercurrent extractor continuously decanting hydrazine-acid-layers from aqueous layers to effect an extraction of the hydrazine from the aqueous layer and thereafter separating the hydrazine from the organicacid and recycling the organic acid to the extracpages; 2 Q 3;"a 1 d 5Q. Wiley and Sons, Inc, 1951, New 

1. AN EXTRACTION PROCESS FOR DEHYDRATING AQUEOUS HYDRAZINE WHICH COMPRISES MIXING AN ORGANIC ACID HAVING AN IONIZATION CONSTANT OF NOT MORE THAN 1.3X10-10 AT 25*C. WITH THE AQUEOUS HYDRAZINE MIXTURE AND DECANTING A HYDRAZINE-ACID LAYER FROM THE AQUEOUS MIXTURE. 